This question should be expected as it can be fairly common in an interview, especially if the interviewer is strongly considering you for the position that you are interviewing for. There should not be any problem in answering this question unless you think that you might have a problem getting to work on time. Even if that is the case, you should not be concerned about answering that question as long as you are prepared. Anytime that you are applying for a job you should give thought in advance to how you will get to and from work so that you can arrive on time. If you have done this you should have a well prepared plan so that you will be able to honestly answer this question and indicate that there will be no problems that would make it difficult for you to arrive at work on time.
You should not answer this question by going into great details about car problems you have had, the unreliability of the public transportation system or the fact that your alarm clock sometimes does not work. This is not what the interviewer wants to hear. They are looking for reassurance that you will be a reliable employee who will arrive at work well in advance of the time you are to begin your duties.
If you have not already given some thought to how you will get to work and ensure that you get there on time, now is certainly the time to begin mapping out a plan. This is not only for the benefit of the employer but also for your own benefit as well. If you have not given thought to how you will arrive at work on time then it is likely that you will experience problems at some point that could make it difficult for you to get to work on time.
In the event that you experienced problems in the past with arriving at work on time you should be prepared to explain how you have rectified this situation because it very well could come out when the employer performs a reference check. You do not want to provide conflicting information and leave it unexplained, risking the possible chance of losing the job because it appears that you have been less than truthful in your responses.